Energy-based design of structures using modified force analogy method

Energy due to earthquake excitations is used to evaluate the performance of a structure. This energy is derived analytically based on the force analogy method, which uses only initial stiffness with changing displacement to accurately capture the inelastic material behaviour. However, numerical calculation using the classical force analogy method considers mass matrices that are invertible, and therefore it is not appropriate for use in analysing real structures where rotational mass moment of inertia is generally ignored. In this research, derivation of the force analogy method is modified to analyse real moment-resisting frames using static condensation. Using this modified force analogy method in the condensed form significantly reduces the size of the structural problem because a large number of rotational degrees of freedom can be condensed. Numerical simulation is then performed to analyse the dynamic response of a six-storey moment-resisting frame and the concept of performance based design is used to improve the structural performance in terms of energy dissipation 'demand' at each plastic hinge. Results show that the amount of total plastic energy dissipation remains about the same for structures with similar frequency contents. This is significant because it shows that understanding the flow of energy in the structure is important in improving structural performance under earthquake excitations. Copyright (C) 2003 John Wiley Sons, Ltd.